1. Field
The present disclosure relates generally to aircraft and, in particular, to a method and apparatus for a fixed-wing aircraft. Still more particularly, the present disclosure relates to a method and apparatus for a fixed-wing aircraft with increased lift.
2. Background
A fixed-wing aircraft is a heavier-than-air vehicle capable of flying in the air. A fixed-wing aircraft is capable of flying due to lift, which is generally generated by the wings of the aircraft. The amount of lift generated by the wings of a fixed-wing aircraft is proportional to the airspeed of the aircraft. At lower airspeeds the wings of an aircraft generate less lift. If the airspeed of the fixed-wing aircraft drops below a stall speed, less lift is created. The amount of lift generated by the aircraft's wings can be a challenge during take-off and landing periods when airspeed levels are lower.
Flaps are generally used on most fixed-wing aircraft to create additional lift during takeoff and landing periods. Flaps increase the camber of the wing airfoil, which increases the coefficient of lift for the wing and ultimately the amount of lift generated. Flaps can also increase the planform area of the wing and thus generate more lift. However, flaps also may add drag and increase the airframe noise generated by the aircraft.
Additionally, the aircraft's angle of attack can be increased to generate additional lift during take-off and landing periods. The angle of attack refers to the angle of an aircraft relative to the ambient flow. Increasing angle of attack during take-off and landing periods can increase the amount of lift generated by the wings. However, there are limits on how much additional lift can be generated. Further, increasing the angle of attack means that the nose of the aircraft is higher than the aft of the aircraft. This can make landing difficult due to restrictions. Also, it may pose a risk of the tail of the aircraft contacting the runway. This risk can be reduced by using longer landing gear, but will result in greater airplane weight.
Further, flow control may be employed to enhance lift capability during aircraft takeoff and landing. Ambient air flowing over the surface of a wing or a flap may not turn around and follow the entire upper surface of the wing or flap. This lack of turning tends to create a separation pocket or a lack of attachment of the flow around the upper surface of the wing or flap. The separation pocket decreases the amount of lift generated by the aircraft.
Flow control can be used to enhance lift performance by using a fluidic source, such as bleed air from an engine or a special purpose compressor. Airflow is ejected out of the aircraft from across the top of the wings or flaps in the general streamwise direction. These ejected air streams impart momentum into the flow. This momentum causes the flow to better turn around and follow the surface of the wing and the flap. Consequently, circulation increases around the entire wing and higher lift is obtained.
However, current methods of airflow control require substantial amounts of ejected airflow to achieve meaningful design targets. The aircraft engines can be used to supply air for actuation by “bleeding” compressed air from inside the engine, but design targets require substantial amount of bleed air. The requirement of engine bleed impacts the size and efficiency of the aircraft engines. The larger the bleed requirement, the larger and heavier the engine needed. Larger and heavier engines lead to an increase in aircraft gross weight and engine cost. In addition, bleed requirements reduce the efficiency of the engines. Alternatively, a separate air compressor can also be used in conjunction with a duct delivery system to supply the air for actuation. However, the addition of separate air compressors also leads to additional weight.
Accordingly, it would be advantageous to have a method and apparatus which takes into account one or more of the issues discussed above as well as possibly other issues.